题目内容
Experts have been warning _______ of the health risks caused by passive smoking.
A. at a time B. at one time C. for some time D. for the time
C
考查词组辨析。at a time“每次;依次”;at one time “曾经;一度”;for some time“一段时间”;for the time“暂时;眼下”。
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